Transmission joints are used to angularly connect a drive shaft and a driven shaft, and to permit movement and tilt of the shaft axes.
More specifically, transmission joints comprise a tubular coupling member with a hub angularly integral with the drive shaft; and a ring positioned radially outwards of the hub and angularly integral with the driven shaft.
More specifically, the joints may comprise a single coupling member, with the hub and ring connected directly to the drive shaft and driven shaft.
Alternatively, the joints may comprise a number of coupling members angularly integral with one another; in which case, the hub of one of the coupling members is connected to the drive shaft, and the hub of another of the coupling members is connected to the driven shaft.
The coupling member also comprises a thin-walled portion, or so-called diaphragm, interposed radially between the hub and ring and elongated in a direction perpendicular to the drive and driven shaft axes.
Diaphragms are known, for example, as described in Patent BE-456920, in which the profile of the diaphragm comprises, from the hub to the ring, a portion decreasing in thickness and a portion increasing in thickness.
More specifically, the profile is asymmetrical with respect to the extension direction of the diaphragm.
Diaphragms are also known, for example, as described in Patent U.S. Pat. No. 5,158,504, in which the profile is symmetrical with respect to the extension direction of the diaphragm.
More specifically, the profile of these diaphragms comprises, from the hub to the ring, a portion decreasing in thickness and a portion increasing in thickness.
The diaphragm profile of known joints provides, in operating conditions, for transmitting a predetermined torque from the drive shaft to the driven shaft with a wide margin of safety, and for maintaining below a predetermined value the fatigue stress caused by periodic variations in the mutual position of the drive and driven shaft axes.
The known joints are less than satisfactory, on account of the known diaphragm profile failing to minimize the weight and overall size of the joint.
In other words, it possible to improve the diaphragm profile in such a way as to reduce the weight and, hence, overall size of the joint as compared with known solutions, while at the same time maintaining the same margin of safety as regards torque transmission and reduction of fatigue stress caused by periodic variations in the mutual position of the drive and driven shaft axes.
It is also possible, by appropriately designing the diaphragm profile, to reduce the weight and, hence, overall size of the joint, while at the same time reducing buckling phenomena caused when the thin-walled diaphragm is subjected to the twisting moment transmitted by the drive shaft.
Finally, it is possible, by appropriately designing the diaphragm profile, to reduce in-service generation of forced oscillations caused by resonance phenomena between the natural frequencies of the system containing the diaphragm, and the rotation frequencies of the drive or driven shaft.